The present invention relates to electronic musical instruments which employ storage means such as a memory and generate musical tones through the access of the storage means.
Conventional electronic musical instruments have performance data input means such as a keyboard; control means which generates control parameters such as a command for triggering the musical tone generation in response to the input data inputted through the performance data input means; and a tone generator which generates musical tones based on the control parameters. Generally, the tone generator provides registers for storing musical tone parameters such as a current amplitude value of the musical tone waveform and a state of the envelope waveform of the generated musical tone. In the tone generator, calculation operations are sequentially executed based on these stored musical tone parameters and the musical tone parameters are sequentially updated based on the calculated result. Through these operations, the tone generation of the musical tone waveform designated by the control means is carried out. Furthermore, in general electronic musical instrument, a RAM (Random Access Memory) is provided as a storage means for storing the control parameters mentioned above and is used by the control means.
Meanwhile, there are cases in which the control means observes the state of the musical tone generation by the tone generator and controls the operation of the tone generator based on the observation. For example, such a case appears in the electronic musical instruments which have a plurality of sound channels and are capable of generating a plurality of musical tones simultaneously and independently by using the sound channels. In these electronic musical instruments, when a new key-on event is detected from the keyboard, the control means selects one of the sound channels through which the musical tone having the lowest envelope value is generated and assigns the selected sound channel for generating the musical tone corresponding to the new key-on event. In such a case, the control means of the conventional electronic musical instrument should read out the musical tone parameters which indicate the state of the musical tone generation and are stored in the control registers of the tone generator. Such an access operation is very heavy load for the control means and therefore it is difficult to provide a high-performance electronic musical instrument. Furthermore, in the case where the number of the sound channels of the tone generator is large, a large number of registers should be provided in the tone generator for storing the musical tone parameters and a large scale control circuit should be provided for controlling the access of the registers. Therefore, the electronic musical instrument becomes high cost.
Furthermore, there are cases in which the same musical tones are repeatedly generated to obtain a sound having a special effects such as a echo sound. In these case, the control means should generate the musical tone parameters every time each one of the musical tones is generated by the tone generator although there are few difference between the musical tone parameters to be generated and the musical tone parameters which have been previously generated.